Several techniques are currently employed to clad materials. These include techniques such as extrusion, rolling, electroplating, weld forming, explosive bonding and the like. Among these techniques extrusion and rolling are sensitive to variable flow stresses of the two materials and require strenuous optimization of processing parameters. Typical defects or challenges to be addressed in using these techniques include non-uniform thicknesses, porous interfaces, lack of metallurgical bonding, etc. and it especially becomes challenging when working with anisotropic hexagonal close packed (HCP) material such as magnesium, titanium or zirconium. The other aforementioned techniques are slow batch processes and unable to control the graded interface or create the desired texture in the final component.
Magnesium is a desirable material for lightweight structures is limited by its corrosion resistance, but cladding it with aluminum or similar material will significantly improve the corrosion resistance and its ability to join with other material systems. Several technical challenges arise when forming such structure such as controlling the texture of the magnesium such that the asymmetry in mechanical properties under compression and tension is eliminated, the preferred grain size of the magnesium is less than 5 micron with an aluminum cladding bonded to the magnesium and the same time forms a graded interface to minimize the corrosion rate in the system. The present disclosure provides a methodology that allows for making structures with specified cladding as well as making structures that have desired shapes and microstructural and mechanical characteristics that existing methodologies struggle to provide.
To meet these needs a process has been developed wherein functionally graded claddings and coatings are produced in a single step with tailored physical properties (such as microstructure, mechanical, electrical, thermal, etc.) and at the same time provide high corrosion resistance. Typically clad materials are preferred material systems for engineering applications, as one metal/alloy often does not satisfy the required application conditions. The major advantage of cladding is the ability to tailor properties such that the surface has a different chemical composition and properties relative to the core. For example aluminum clad copper wires provide excellent conductivity with improved corrosion life. Clad materials also offer minimal use of expensive materials, such as high temperature materials, and at the same time retain the desired physical properties such as thermal conductivity.
Over the past several years researchers at the Pacific Northwest National Laboratory have developed a novel Shear Assisted Processing and Extrusion (ShAPE™) technique which uses a rotating ram as opposed to the axially fed ram used in the conventional extrusion process. As described in the previously cited and incorporated references, in some embodiments the ram face contains spiral scroll features which when brought into contact with a solid billet and a forging load is applied, significant heating occurs due to friction, thus softening the underlying billet material. The combined action of the forging load together with the rotating action of the ram face, force the underlying material to flow plastically. The scroll features on the ram face help in the material flow and help in controlling the texture.
We have successfully demonstrated the scalability of this process, and we were able to alter and control the texture, grain size and also uniformly disperse the secondary particles by changing a few process parameters and at loads/pressure several orders or magnitude lower than conventional extrusion. We have now expanded applications of this tool and process to generate cladded materials by extrusion and to control various features of structures formed by this technique.
This provides significant promise over several of the prior art techniques which are typically employed to clad materials such as extrusion, rolling, electroplating, weld forming, explosive bonding, etc. Extrusion and rolling are sensitive to variable flow stresses of the two materials and require strenuous optimization of processing parameters. Typical defects or challenges to address using these techniques are non-uniform thickness, porous interface, lack of metallurgical bond, etc. and it especially becomes challenging when working with anisotropic HCP material such as magnesium, titanium or zirconium. Typically the aforementioned techniques are performed in a slow batch processes and are unable to control the graded interface or create the desired texture in the final component. Conventional linear extrusions typically have virtually constant crystallographic texture across the wall thickness.
Developing a method for forming extrusions while simultaneously varying the texture across the wall thickness could lead to improved bulk material properties. Such improvement could include but are not limited to increased strength, reduced susceptibility to corrosion and brittleness, Mechanical property improvements through breakdown and dispersion deleterious second phase particles, corrosion resistance though elimination of galvanically unfavorable second phases and precipitates, and extrusion of brittle intermetallic materials not possible by conventional means among them.
The purpose of the foregoing abstract is to enable the United States Patent and Trademark Office and the public generally, especially the scientists, engineers, and practitioners in the art who are not familiar with patent or legal terms or phraseology, to determine quickly from a cursory inspection the nature and essence of the technical disclosure of the application. The abstract is neither intended to define the invention of the application, which is measured by the claims, nor is it intended to be limiting as to the scope of the invention in any way.
Various advantages and novel features of the present invention are described herein and will become further readily apparent to those skilled in this art from the following detailed description. In the preceding and following descriptions I have shown and described only the preferred embodiment of the invention, by way of illustration of the best mode contemplated for carrying out the invention. As will be realized, the invention is capable of modification in various respects without departing from the invention. Accordingly, the drawings and description of the preferred embodiment set forth hereafter are to be regarded as illustrative in nature, and not as restrictive.